The appearance of a younger child, brother or sister, may represent a decisive moment in the existence of the first born. The possibly violent exit from the Eden-like universe of primary narcissism, of limitless self-love, via the birth of a second child represents a structuring experience, which forces the repositioning of the Ego in a manner similar to the hierarchic positioning within the primitive horde. In this context, the discovery and exploration of the other seems to become the main form of access to the construction of the Ego in the presence of an alterity that carries the mark of a narcissistic wound.